1. Technical Field
The present invention relates to wireless communication systems and, in particular, to beamforming methods and systems.
2. Description of the Related Art
For frequencies of about 60 GHz, beamforming techniques present exceptional options for exploiting a unique combination of high free space path loss and the possibility of increased antenna directivity for a given antenna aperture area to improve a link budget. However, channel conditions can vary between beams. To address the problem of changing channel conditions causing a change in the optimal pair of beams employed for communication, prior work has suggested the use of adaptive beamforming techniques. Such techniques require the accurate estimation of the phase and amplitude of signals at the receiver (RX), and subsequent feedback to the transmitter (Tx). These techniques enable the “tracking” of the best pair of beams for communication. However, adaptive beamforming imposes certain hardware requirements on stations, such as requirements for fast and accurate estimation of the phase of the signal at the receiver, which increases their complexity and reduces their applicability.
To address the problem of link blockage, in which data signal transmission is blocked due to poor channel conditions, prior work has suggested using multiple, distributed receiver antennas, for example, via base station diversity or antenna sub-assembly diversity, and multi-hop relays. In the presence of link blockage, it is likely that the beam utilized to transmit data to a current receiver is blocked, but beams to another receiver, for example, either another antenna, node or base station, may still be usable. In such cases, the signals or packets received on the secondary antenna, node or base station will then have to be forwarded to the intended receiver. While such techniques are likely to address the problem, they place additional requirements on the network, such as co-ordination between base stations or between relays, or on the transcievers themselves, such as an additional antenna sub-assembly, which reduces their applicability.